Those mechanical assemblies that necessarily must be constructed from discrete parts which operate through a wall and must be machined by succesive chucking operations often result in an excessive tolerance build-up. Reliable repetitive operation of pressure responsive devices through walls employing an operator and a negative rate spring, requires precise motion through the wall. The overall tolerance through the wall, the operator and the negative rate spring must be in the +/- one-one thousandths of an inch range.
In a pressure responsive device of this general type, a disc or belleville spring is positioned in a seat and deflected by a ring bearing on its inner edge. The ring is actuated by an operator through a wall which is in turn actuated by pressure bearing on a diaphragm resting on a plate. The operator is a pin which moves in a direction which is normal to the plane of the disc. The total travel of the disc spring in this assembly must be precisely established in assembly to match the force-deflection spring characteristics of the disc spring for the operating pressures expected up to the proof pressure.
In the past, the precise control of the operator's travel was dependent upon either shimming of or machine trimming parts in assembly. The tolerances provided by state of the art CNC machines because of the several chuckings required were invariably excessive in the final assembly. Another travel variable was introduced by the forming of parts from sheet metal which necessarily had its grain warpage running at right angles to the direction of travel. It would be far superior if the disc or spring and operator pin were fabricated to matched dimensions and assembled into non repairable assemblies with predictable characteristics for their operating lifetime.